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__Physical Quantities: __

__Physical Quantities:__

In physical science, we commonly deal with quantities such as pressure, volume, mass, temperature, current, etc. These quantities are known as physical quantities.

A physical quantity has two components, namely,

**and its**__numerical value__**and is written as,**__unit__Physical quantity |
= |
Numerical value |
unit |

Force |
= |
5 |
Newton |

Here Physical quantity

**Newton**and its numerical value**5**Physical quantity |
Name of the Unit |
Symbol |

Length | Centimeter | cm |

Mass | Gram | gm |

Time | Second | S |

Electric Current | Ampere | Amp |

Temperature | Kelvin | ^{0}K |

Physical quantity |
Name of the Unit |
Symbol |

Length | Meter | m |

Mass | Kilogram | Kg |

Time | Second | S |

Electric Current | Ampere | Amp |

Temperature | Kelvin | ^{0}K |

Physical quantity |
Name of the Unit |

Length | L |

Mass | M |

Time | T |

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__Definition of Seven Base Physical Quantities:__

__Definition of Seven Base Physical Quantities:__

**The metre is the length of path traveled by light in vacuum during a time interval 1/299 792 458 of a second.**

__Metre:__1. Area |

**Area = Length × Length**

Thus the unit of Area = Unit of Length × Unit of Length

Unit of Area in

**C.G.S**. System =**cm × cm = cm²**
Unit of Area in

**S.I.**System is =**m × m = m²**
Dimension of Area =

**L × L = [L]²**2. Volume |

**Volume (V) = Length × Length × Length.**

Thus the unit of Volume = Unit of Length × Unit of Length × Unit of Length.

Unit of Area in C.G.S. System =

**cm × cm × cm**=**cm³**
Unit of Area in S.I. System is =

**m × m × m**=**m³**
Dimension of Area =

**L × L × L**=**[L³]**3. Density |

**Density (d) = Mass/Volume**

Thus the unit of Area = Unit of Mass/Unit of Volume.

Unit of Area in C.G.S. System =

**gm/cm³ = gm cm⁻³**
Unit of Area in S.I. System is =

**Kg/m³ = Kg m⁻³**
Dimension of Area =

**[M]/[L³] = [M L⁻³]**4. Force |

From the

**,**__Newton Second Low of Motion__**Force = Mass × Acceleration.**
or, Force = Mass × Velocity/Time

or, Force = Mass × (Length/Time) /Time,

Here Velocity = Length/Time

or, Force = Mass × (Length/Time²)

Thus the unit of Force in C.G.S. System, =Unit of Mass × (Unit of Length/Unit of Time²)

=

**gm****×****cm****/****sec**^{2}
=

**gm****cm****/****sec**^{2}
or,

**gm****cm****sec**^{-2}**or**

__Dyne.__
Again in the same way Unit of Force in S.I System,

=

**Kg****m****/****sec**^{2}
or

**Kg****m****sec**^{-2}
or

__Newton.__
From the above discussion dimension of Force, = dimension of Mass × dimension of Length/dimension of Time².

Thus the dimension of Force =

**[M****L**T^{-2}**]**Conversation Newton to Dyne |

**1 Newton =**=

**Kg**

**m**

**/**

**sec**

^{2}
= (1

**Kg**× 1**m**)/(1**sec**)²
We know that, 1 Kg = 10³ gm and 1 m = 10² cm

Thus,

**1 Newton**= (10³gm × 10² cm)/(1 sec)²
= 10⁵

**gm****cm****/****sec**^{2}**=**

**10**

^{5}**Dyne**

5. Work |

We Know that,

**Work (W) = Force(F) × Displacement(d).**
Thus, the unit Work = unit of Force × unit of Displacement(d)

∴ Unit of Work in C.G.S. System, = (

**gm****cm****/****sec**) ×^{2}**cm**
or,

**gm****cm**^{2}**/****sec**^{2}
or,

**gm****cm**^{2}**sec**^{-2}
or,

**erg.**
And unit of work in S.I. system = (

**Kg****m****/****sec**) ×^{2}**m**
or,

or,

**Kg****m**^{2}**/****sec**^{2}**Kg****m**^{2}**sec**^{-2}or,

**Joule.**
From the above discussion dimension of Work, = dimension of Mass × {(dimension of Length)²/dimension of Time²}.

Thus dimension of Work =

**[M****L**T^{2}^{-2}**]**Conversation Joule to erg |

**1 Joule**= 1 Kg m²/sec²

= (1 Kg × 1 m² )/1 sec².

We know that, 1 Kg = 10³ gm and 1 m = 10² cm.

Thus, 1 Joule = {10³ gm × (10²)² cm}/1 sec²

= 10⁷ gram cm²/sec²

=

**10⁷ erg.**6. Work |

__The ability to doing work is termed as Energy__. Thus, the unit and dimension of

**energy**and

**work**is same.

Unit of Energy in C.G.S System is

**erg**and S.I. System is**Joule.**